This is a super important point, but someone touched on it above. A major part of fitness is the lifestyle aspect, whether it's finding activities that combine social activity and fitness (sports!) or taking things you do already (like commuting) and making those physical (living where you can walk to commute instead of driving). None of this is easy, and yes, this lifestyle means you have to want to make the change. But for me I'm not trying to stay fit to look fancy or buy new clothes. I'm trying to stay fit and build patterns at 30 so that I'm still able to learn new tech and play with my great grand kids at 90. I look at this as investing in my future and my investment in fitness now is going to pay more mental health dividends than any amount of money. Speaking of course from a position where I have the privilege to make these choices.